1. Field of the Invention
This invention relates to a fuse element used in integrated circuit (IC) devices and, more particularly, to a fuse structure and method of making the fuse which employs a local change in electrical conductivity of a film in contact with metal lines.
2. Description of Related Art
Fuses are used in integrated circuit devices such as semiconductor chips to provide redundancy, electrical chip identification and customization of function. For designs having three or more layers of wiring, the fuses are typically formed from a segment of one of the wiring layers, e.g., the xe2x80x9clast metalxe2x80x9d or xe2x80x9clast metal minus onexe2x80x9d wiring layer. Fusing, i.e., deletion of a segment of metal fuse line, is accomplished by exposing the segment to a short, high intensity pulse of xe2x80x9clightxe2x80x9d from an infra-red laser. The molten metal then boils, vaporizes or explodes out of its oxide surroundings, disrupting line continuity and causing high electrical resistance. A sensing circuit is used to detect fuse segment resistance. Sense circuits can be designed to detect that fusing has occurred when line resistance increases or line resistance decreases.
Critically, the dielectric surrounding the fuse must act much like a pressure vessel, i.e., holding the fuse captive until sufficient pressure is achieved during the superheating phase to cause the fuse link to explode through the weakest wall of the pressure vessel and instantaneously boil away. If pressure is released too soon, the fuse melts and extrudes to the surface through the cracks in the dielectric. Any porous materials in contact with the fuse link will experience compression of the voids with subsequent loss of pressure. If material is a polymer, actual reduction in mass occurs as Tg, the glass transition temperature (typically less than 500xc2x0 C. for polyimide-like materials) is exceeded and the voids are expelled.
Prior art includes U.S. Pat. Nos. 5,523,253 and 5,420,455 to Gilmour et al.; U.S. Pat. No. 5,591,285 to Afzali-Ardakani et al.; U.S. Pat. No. 5,202,061 to Angelopoulos et al.; U.S. Pat. No. 4,590,258 to Linde et al.; U.S. Pat. No. 5,115,095 to Babich et al., U.S. Pat. No. 5,608,257 to Lee et al. and U.S. Pat. No. 5,795,819 to Motsiff et al., all assigned to the assignee of the instant invention. Other art includes U.S. Pat. No. 5,705,849 to Zheng et al., U.S. Pat. No. 5,811,869 to Sevyedy et al., U.S. Pat. No. 5,834,824 to Shepherd et al., U.S. Pat. No. 5,376,502 to Novak et al., U.S. Pat. No. 5,852,323 to Conn, U.S. Pat. No. 5,130,392 to Schwalm et al., U.S. Pat. No. 5,463,014 to Epstein et al., U.S. Pat. No. 5,777,540 to Dedert et al., U.S. Pat. No. 5,663,702 to Shaw, Jr. et al., U.S. Pat. No. 5,855,755 to Murphy et al.
It would be advantageous to eliminate the above described problems by changing the fuse structure and method of making the fuse to avoid the need to physically blow fuses.
Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide a fuse structure for integrated circuit devices which eliminates the problems of physically blowing fuses.
It is another object of the present invention to provide a method of making such a fuse structure.
A further object of the invention is to provide a method of utilizing a fuse structure in which there is no physical disruption to the fuse.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.
The above and other objects and advantages, which will be apparent to one of skill in the art, are achieved in the present invention which is directed to, in a first aspect, a method of programming a device comprising first providing a device having an open circuit comprising a pair of wires having ends thereof separated by a gap. Thereafter a polymer block is formed over the separated ends of the wire. The polymer block is then exposed to an energy beam in order to increase the conductivity of the polymer and electrically connect the wire ends. Preferably, the polymer block comprises a polyimide capable of carbonizing when exposed to an ion or other energy beam for a sufficient time so as to become electrically conductive. More preferably, the polymer block comprises a photoconductive polymer material, and most preferably, the polymer block comprises a polymer/onium salt mixture. Byway of example, the polymer block may comprise a polyaniline polymer doped with a triphenylsufonium salt. The method may further comprise providing a low dielectric constant (low k) nanopore/nanofoam dielectric material adjacent the wire ends.
In a related aspect, the present invention provides a method of making a fuse for a semiconductor device comprising initially providing an insulating substrate having a surface. Thereafter, a conductive line pair is formed on the surface of the insulating substrate, the conductive line pair having spaced ends. Finally, there is formed over the insulating substrate and between the conductive line pair ends a layer of a polymer capable of carbonizing when exposed to an ion or other energy beam for a sufficient time so as to become electrically conductive. Preferably, the polymer comprises a polyimide, more preferably, a polymer/onium salt mixture, and most preferably, a polyaniline polymer doped with a triphenylsufonium salt.
The method may further include the step of exposing the polymer in a region between the spaced ends of the conductive line pair to an energy beam to increase the conductivity of the polymer thereby forming a conductive connection between each line of the conductive line pair.
In yet another related aspect, the present invention provides a method of forming an antifuse comprising forming a first conductor in a dielectric layer, forming a second conductor in the dielectric layer and forming a polymer layer over the first and second conductors. Thereafter, the polymer layer is exposed in a region overlapping at least a portion of both the first and second conductors to an energy beam to lower the electrical resistance of the polymer in the region and electrically connect the first and second conductors. Preferably, the dielectric layer comprises a low k dielectric foam. The polymer layer may comprise a polyimide and the first and second conductors may comprise aluminum or copper.
In another aspect, the present invention provides a fusible link for a semiconductor device comprising an insulating substrate and a conductive line pair on the surface of the insulating substrate, with the conductive line pair having spaced ends. A polymer is disposed over the insulating substrate and between the conductive line pair ends. The polymer is capable of being changed from a non-conductive to a conductive state upon exposure to an energy beam. Preferably, the polymer comprises a polyimide, more preferably, a polymer/onium salt mixture, most preferably, a polyaniline polymer doped with a triphenylsufonium salt. The link may further comprise a low k nanopore/nanofoam dielectric material adjacent the conductive line ends.